Technical Field
The present disclosure relates to microelectromechanical microphones and to processes for manufacturing microelectromechanical microphones.
Description of the Related Art
Microelectromechanical microphones are known, which comprise a first chip incorporating a microelectromechanical electroacoustic membrane transducer, and a second chip incorporating a control circuit or ASIC (Application-Specific Integrated Circuit). The electroacoustic transducer converts incident acoustic waves, which cause vibrations of a membrane, into electrical signals. For example, the membrane may be capacitively coupled to a reference electrode. The deformations of the membrane modify the capacitive coupling, which may be easily detected with a charge-amplifier circuit of the control circuit. The control circuit comprises signal-processing stages (for example, the charge-amplifier circuit) and components suitable for interacting with and enabling operation of the microelectromechanical microphone, in particular transduction of the acoustic signals.
The first chip and the second chip are housed within a same package structure for electronic devices, which generally includes a supporting substrate and a cap of plastic or metal material.
The substrate may be a polymeric or ceramic substrate, for example of the LGA (Land-Grid Array) type and is provided with connection structures (pads and lines) for electrical connection of the first chip and of the second chip, which are arranged alongside one another. Further, the substrate has an opening, also referred to as “sound port”, which enables transmission of the acoustic signals from outside of the package structure to the transducer that is inside the package structure.
The cap is bonded to the substrate and may have a dual function of protection and definition of an acoustic chamber and, for this reason, may have a determining effect upon the performance of the microelectromechanical microphone.
The attention directed to the development and integration of microelectromechanical sensors has been progressively increasing, in step with the spread of portable electronic devices such as smartphones and tablets or other electronic devices of the so-called “wearable” type. The at times tumultuous development of products of this kind may, in some cases, set down specifications that are contrasting or difficult to reconcile. On the one hand, for example, there is the desire to offer microelectromechanical transducers with increasingly higher levels of performance to meet the specifications of users. This generally leads to providing chips of larger dimensions both for the microelectromechanical transducer and for the control circuit. On the other hand, instead, there is the contrasting desire to reduce more and more the dimensions of microelectromechanical microphones, especially in portable and wearable systems.
Additionally, fitting two chips, such as a control ASIC and a microelectromechanical transducers in the package can be difficult. The size of the chip incorporating the control ASIC is often reduced for allowing greater space for the chip incorporating the transducer. However, there is a desirable to increase the size of the chip incorporating the ASIC to make available a larger number of functions for control and processing of the transduced signals.